In the first five years of this funded project, physiological studies using regional cerebral blood flow, event-related potentials, and positron emission tomography have separately suggested alterations of neural organization, particularly in the left hemisphere, in dyslexic individuals. The current proposal aims to unify the ERP and PET physiological methods as well as MRI profiles into an integrated anatomical and behavioral description of the neurobehavioral substrate of dyslexia. Accordingly, physiological measurements would be made during the performance of cognitive tasks chosen to elicit specific, localized regions of activation. In three groups of subjects (dyslexics and normal readers) with well-documented childhood reading data, four tasks will be measured across these methods. In Experiment 1, a group of 10 will perform two auditory linguistic activation tasks during PET scanning. In Experiment 2, a group of 40 will perform crossmodal linguistic activation tasks during simultaneouS PET and ERP measurement. MR images on all PET scan participants will allow reconstruction and measurement of the temporal plana and caudates to determine the anatomical characterization of dyslexia. In Experiment 3, another group of 40 will perform visual letter and word discrimination paradigms, again during simultaneouS ERP and PET measurement, with MR images for anatomical reconstruction. In Experiment 4, 100 subjects varying in reading disability, their spouses, and 150 of their children will undergo event-related potential measurement during various visual tasks, allowing direct comparison to their parent data as well as to the childhood longitudinal normal, reading impaired, and at-risk samples collected in the first five years of our current program project. We will specifically test the hypothesis of a unitary, underlying physiological deficit manifest in each of these physiological measurement domains.